1. Field of the Invention
The present invention relates to a semiconductor light-receiving device, and particularly to a semiconductor light-receiving device in optical communication and optical transmission technologies.
2. Discussion of the Background
In the instruments utilizing semiconductors, such as computers and communication instruments, semiconductors such as IC, mounted on the instruments, become larger in capacity year by year. With such a development, an increase of the capacity in signal transmission means has been required. This tendency extends to the peripheries of terminal computers of the communication, and memory, where having a large capacity has been required more and more. Particularly, the demand for optical disks having portability has increased more and more, a larger capacity has been more and more required, and various systems have been investigated and developed.
Of these systems, a more practically used one is a system wherein a storage spot area is reduced by shortening a wavelength of the light source. For this system, a system of using a blue semiconductor laser is promising. Hitherto, a DVD using a red semiconductor laser has been on the market, and in this case, a silicon photodiode has been used as a light-receiving element. This photodiode has a high sensitivity to a red color and has high reliability. Also, by making the most of the merit for mass production, it becomes possible to produce the photodiode at a very low cost by improving the process, etc.
As a photodiode used for reproducing optical disk signals, for example, an example shown by Japanese Patent Laid-Open No. 270744/1998 is known. This example is shown in FIG. 7. In FIG. 7, element 81 is a P-type high specific resistance semiconductor substrate, 72 and 75 are P-type separating diffusion regions, 73 is a P-type embedding diffusion region, 74 is an N-type epitaxial layer, 76 is an N-type diffusion region, 82 is an oxide film, and 83 is an electrode for taking out a substrate potential. The P-type separating diffusion regions 72 and 75 are disposed such that they electrically separate the N-type epitaxial layer 74 into plural regions and that the outsides of the regions of both ends thereof in FIG. 7 are electrically separated. Each separated region functions as a photodiode (photodetecting portion).
However, since the N-type diffusion region 76 of each photodiode is formed on substantially the whole surface of the light-receiving region, when the wavelength becomes short, the absorption in the N-type diffusion region 76 becomes large. FIG. 8 is a characteristic view showing a relation between the depth from an incident surface of the N-type diffusion region 76 and the intensity of a transmitted light when a blue light of 400 nm enters silicon. As shown in FIG. 8, as the depth becomes deeper, the intensity of the transmitted light is greatly reduced. Accordingly, by the structure of the photodiode of the related art shown in FIG. 7, a sufficient sensitivity cannot be obtained to a blue light having a short wavelength.
Thus, it may be considered that by making the thickness of the N-type diffusion region 76 extremely thin as, for example, about 0.1 μm, an excessive loss by the light absorption is reduced, but because high process controlling properties are required, there is a problem of increasing the cost.
As described above, when the light absorption becomes large in the surface diffusion layer of a semiconductor light-receiving element, there are problems that the intensity of a transmitted light is reduced and that the sensitivity characteristics of a light-receiving element are deteriorated. Also, although it may be considered that by making the thickness of the surface diffusion layer extremely thin, an excessive loss of the light absorption is reduced, but there is a problem of increasing the cost because high process controlling properties are required.